1. Field of the Invention
The present invention relates to a semiconductor chip and a semiconductor device including the semiconductor chip, and particularly relates to a semiconductor chip in which a data output buffer and a strobe output buffer are provided to output a data signal and a strobe signal, respectively, and a semiconductor device including the semiconductor chip.
2. Description of Related Art
In a semiconductor chip having a high data transfer rate, such as DRAM (Dynamic Random Access Memory), when a data signal is output to outside in synchronization with a strobe signal that indicates an output timing of the data signal. The strobe signal enables a controller, which receives the data signal, to capture the data signal in synchronization with the strobe signal. Therefore, even when the data transfer rate is high, it is possible to accurately capture the data signal.
Because the data or strobe signal is output from a respective output buffer to the outside of the semiconductor chip, the output buffer employs a transistor having a high drive capability. Therefore, the output buffer can easily cause power-supply noise in association with switching. In order to prevent such power-supply noise from spreading to other internal circuits via power-supply wirings, a power-supply pad for the output buffer may be provided separately from power-supply pads for the other internal circuits (See Japanese Patent Application Laid-Open No. 2009-283673).
However, the power-supply noise associated with the switching of the output buffer can affect other output buffers. Particularly when the same power source is shared by a data output buffer, which outputs a data signal, and a strobe output buffer, which outputs a strobe signal, as shown in FIG. 12 of Japanese Patent Application Laid-Open No. 2009-283673, the power-supply noise, occurred in association with operation of the data output buffer, could spread to the strobe output buffer, possibly leading to a decline in the quality of the strobe signal.
Because the strobe signal is a reference signal that indicates a timing to capture data for the controller, the quality of the strobe signal is required to be higher than other signals. Accordingly, it is hoped that measures will be taken on a semiconductor chip and a circuit board on which the semiconductor chip is mounted in order to prevent the power-supply noise associated with the switching of the output buffer from spreading to the strobe output buffer.